$opacity = 0,
           10,
           20,
           40,
           75

for oat in $opacity
  .o-{oat}
    opacity (oat/100)


$opactiy-hover = 50,
                 70

for oth in $opactiy-hover
  .o-hover-{oth}
    opacity 1
    &:hover
      opacity (oth/100)


.o-active-50
  &:active
    opacity .5